The present invention relates to a method of quantifying atmospheric hydroperoxyl radical. More specifically, the present invention relates to using solution phase chemiluminescence detection for the quantification of hydroperoxyl radical found in the atmosphere.
Hydroperoxyl radical in the atmosphere plays an important role in the formation and transformation of numerous atmospheric chemicals. In particular, hydroperoxyl radical plays a role in the formation of ozone, well known as a protective agent against the harmful effects of solar radiation.
Accordingly, there has been much interest in quantifying hydroperoxyl radical in the atmosphere. For example, Cantrell et al. uses a chain-amplified gas-phase process to quantify atmospheric levels of hydroperoxyl radicals. Cantrell uses the reaction of hydroperoxyl radical with NO to produce NO2, the species that is ultimately measured in the method. The accuracy of the Cantrell method is dependent on precise calculations regarding the NO2 amplification process. The Cantrell method is also subject to interference from such atmospheric species as ozone, peroxyacetyl nitrate (PAN), and NO2.
Similarly, Creasey et al and Brune et al have shown that hydroperoxyl radical can be measured in the gas-phase by reaction of the radical with excess NO, followed by detection of hydroxyl radical using laser-induced fluorescence (LIF) at 308 nm.
Milhelcic et al report measurement of hydroperoxyl radical using ESR spectroscopy after trapping the radicals in a solid D2O matrix at 77 K. The method used by Milhelcic et al requires the use of a numerical fitting procedure that permits the quantification of HO2 in the presence of organoperoxyl radical.
In addition, the detection of hydroperoxyl radical and its conjugate base, superoxide anion, in solution by reaction of the radical with certain chemiluminescent compounds, is well known. The chemiluminescence produced in solution creates a strong and readily detectable signal without the need for complex amplification procedures. Still further, chemiluminescence methods of detection of hydroperoxyl radical in solution are typically convenient and inexpensive.
The two most popular compounds used for eliciting a chemiluminescent response with hydroperoxyl radical or superoxide anion, i.e., chemiluminescent compounds, are 2-methyl-6-phenyl-3,7-dihydroimidazo[1,2-a]pyrazin-3-one (CLA) and 2-methyl-6-(p-methoxyphenyl)-3,7-dihydroimidazo[1,2-a]pyrazin-3-one (MCLA). A review of chemiluminescent compounds for the detection of hydroperoxyl radical/superoxide anion has been given by Shimomura, et al.
For example, Malbon, et al and Boland, et al report the use of MCLA for the detection of superoxide in natural water systems. The Malbon and Boland procedures quantify superoxide by use of superoxide standards. The superoxide standards are prepared by the photolysis of a benzophenone derivative in aqueous 2-propanol solution.
However, there remains a need for a method capable of quantifying atmospheric hydroperoxyl radical that is convenient, accurate, and inexpensive. For example, none of the above references apply the many benefits of solution-phase chemiluminescence methods of detection to the quantification of atmospheric hydroperoxyl radical.
Accordingly, there is a need for improved methods of quantifying atmospheric hydroperoxyl radical. In particular, there is a need for applying the many advantages of solution phase chemiluminescence detection of hydroperoxyl radical to the quantification of hydroperoxyl radical found in the atmosphere.